Asymmetric wedge JFET, related method and design structure

ABSTRACT

A junction gate field-effect transistor (JFET) for an integrated circuit (IC) chip is provided comprising a source region, a drain region, a lower gate, and a channel, with an insulating shallow trench isolation (STI) region extending from an inner edge of an upper surface of the source region to an inner edge of an upper surface of the drain region, without an intentionally doped region, e.g., an upper gate, coplanar with an upper surface of the IC chip between the source/drain regions. In addition, an asymmetrical quasi-buried upper gate can be included, disposed under a portion of the STI region, but not extending under a portion of the STI region proximate to the drain region. Embodiments of this invention also include providing an implantation layer, under the source region, to reduce R on . A related method and design structure are also disclosed.

TECHNICAL FIELD

Embodiments of this invention relate generally to integrated circuitchips and, more particularly, to a chip including an asymmetric wedgejunction gate field-effect transistor (JFET), a related method anddesign structure.

BACKGROUND

Typically, in semiconductor chip applications, in a field effecttransistor (FET), such as a junction gate field-effect transistor(JFET), there is a relationship between the pinchoff voltage V_(p) (thegate voltage at which the device will no longer conduct between thesource and drain) and the on resistance R_(on) (the linear relationshipbetween drain to source voltage and drain current for low drain tosource voltage). Specifically, current methods of reducing R_(on) havethe effect of increasing V_(p). Therefore, it is difficult to fabricatea JFET device with a low V_(p) while maintaining a low R_(on). Intechnologies with deep shallow trench isolations (STIs) and shallowdiffusions, it is difficult to construct a standard JFET with a lowR_(on) and low V_(p). This is typically due to the fact that the JFETchannel must extend underneath the STI and therefore the shallower gatejunction provides less impact (or no contribution) to turning off thedevice (i.e., V_(p)).

BRIEF SUMMARY

A junction gate field-effect transistor (JFET) for an integrated circuit(IC) chip is provided comprising a source region, a drain region, alower gate, and a channel, with an insulating shallow trench isolation(STI) region extending from an inner edge of an upper surface of thesource region to an inner edge of an upper surface of the drain region,without an intentionally doped region, e.g., an upper gate, coplanarwith an upper surface of the IC chip between the source/drain regions.In addition, an asymmetrical quasi-buried upper gate can be included,the quasi-buried upper gate disposed under a portion of the STI region,but not extending under a portion of the STI region proximate to thedrain region. Embodiments of this invention also include providing animplantation layer, under the source region, to reduce R_(on). A relatedmethod and design structure are also disclosed.

A first aspect of the disclosure provides junction field effecttransistor (JFET) having an upper surface, the JFET comprising: a sourceregion having an upper surface substantially coplanar with the uppersurface of the JFET, the upper surface of the source region having aninner edge and an outer edge; a drain region having an upper surfacesubstantially coplanar with the upper surface of the JFET, the uppersurface of the drain region having an inner edge and an outer edge; achannel region disposed under the source region and the drain region;and a shallow trench isolation (STI) region comprising an insulatormaterial, the STI region having an upper surface substantially coplanarwith the upper surface of the JFET, the upper surface of the STI regionextending from the inner edge of the source region to the inner edge ofthe drain region.

A second aspect of the disclosure provides a method of forming ajunction field effect transistor (JFET), the method comprising: forminga trench in the substrate, the trench having a substantially horizontalbottom surface, a substantially vertical first side and a substantiallyvertical second side; forming a quasi-buried upper gate below thetrench; filling the trench with an insulator material to create ashallow trench isolation (STI) region, wherein the quasi-buried uppergate is disposed under a portion of the STI region such that thequasi-buried upper gate does not extend along a portion of the STIregion proximate to the second side of the trench; forming a lower gateregion below the STI region; forming a channel region disposed betweenthe lower gate and the STI region; forming a source region adjacent tothe first side of the trench; and forming a drain region adjacent to thesecond side of the trench.

A third aspect of the invention provides a final design structureinstantiated in a machine readable medium for designing andmanufacturing a circuit, the final design structure comprising machinereadable instructions for manufacturing at least one circuit and anintegrated circuit, the circuit comprising: a junction field effecttransistor (JFET) including: a source region having an upper surfacesubstantially coplanar with the upper surface of the JFET, the uppersurface of the source region having an inner edge and an outer edge; adrain region having an upper surface substantially coplanar with theupper surface of the JFET, the upper surface of the drain region havingan inner edge and an outer edge; a channel region disposed under thesource region and the drain region; and a shallow trench isolation (STI)region comprising an insulator material, the STI region having an uppersurface substantially coplanar with the upper surface of the JFET, theSTI region extending from the inner edge of the source region to theinner edge of the drain region.

These and other aspects, advantages and salient features of theinvention will become apparent from the following detailed description,which, when taken in conjunction with the annexed drawings, where likeparts are designated by like reference characters throughout thedrawings, disclose embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the inventionwill be better understood by reading the following more particulardescription of the invention in conjunction with the accompanyingdrawings.

FIG. 1 shows a junction gate field-effect transistor (JFET) as known inthe art.

FIGS. 2-6 show various views of a JFET according to embodiments of theinvention.

FIGS. 7-15 show a method of forming a JFET according to embodiments ofthe invention.

FIG. 16 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention, and therefore should not be considered aslimiting the scope of the invention. In the drawings, like numberingrepresents like elements.

DETAILED DESCRIPTION

FIG. 1 shows a junction gate field effect transistor (JFET) 20incorporated into substrate 10 of an integrated circuit (IC) chip(partially shown) as known in the art. JFET 20 can include a deep dopedregion 22, a lower gate 24, a channel region 26, an upper gate 28 and aplurality of shallow trench isolation (STI) regions 30. JFET 20 furtherincludes a source region 32 and a drain region 34. As is known in theart, the depth of deep doped region 22, lower gate 24 and channel region26 can be adjusted as desired.

It is understood that when forming JFET 20, regardless of the depth ofeach layer, each adjacent layer is intentionally doped with an oppositepolarity, i.e., n-type dopants such as phosphorous (P), arsenic (As) orantimony (Sb), or p-type dopants such as boron (B), indium (In) orgallium (Ga), in order to ensure that there is little to no conductionbetween the layers. For example, if deep doped region 22 is doped withn-type dopants, lower gate 24 would be doped with p-type dopants,channel region 26 would be doped with n-type dopants, and upper gate 28would be doped with p-type dopants.

As is shown in FIG. 1, traditional JFETs, such as JFET 20, include anupper gate 28 that has an upper surface that is coplanar with an uppersurface of substrate 10, between source region 32 and drain region 34,with at least a first STI region 30 separating source region 32 fromupper gate 28, and a second STI region 30 separating source region 34from upper gate 28.

FIG. 2 shows a JFET 120 according to an embodiment of this invention.JFET 120 is incorporated into a substrate 110 of an IC chip (partiallyshown). As in JFET 20, JFET 120 includes a deep doped region 122, alower gate 124 and a channel region 126. Again, the depth and width ofeach layer can be adjusted as desired. JFET 120 further includes asource region 132 having an upper surface substantially coplanar withthe upper surface of JFET 120, the upper surface of source region 132having an inner edge 132 a and an outer edge 132 b. JFET 120 furtherincludes a drain region 134 having an upper surface substantiallycoplanar with the upper surface of JFET 120, the upper surface of drainregion 134 having an inner edge 134 a and an outer edge 134 b.

However, in contrast to traditional JFETs, such as JFET 20 shown in FIG.1, JFET 120 does not include an upper gate coplanar with the upper (top)surface of JFET 120. Instead, the region that is coplanar with the uppersurface of JFET 120 between source region 132 and drain region 134 is asingle STI region 136 that comprises insulator material and is notintentionally doped. In other words, a single, uninterrupted STI region136 having an upper surface substantially coplanar with the uppersurface of JFET 120, extends from inner edge 132 a of source region 132to inner edge 134 a of drain region 134. As such, there is no uppergate, e.g., intentionally doped region, between inner edge 132 a ofsource region 132 and inner edge 134 a of drain region 134.

STI region 136 can comprise any now known or later developed insulatormaterial, and can be formed by any commonly known technique for formingan isolation region, such as etching a pattern of trenches in thesilicon, depositing one or more dielectric materials (such as siliconoxide) to fill the trenches, and removing the excess dielectric using atechnique such as chemical-mechanical planarization.

Eliminating the upper gate and the additional STI regions on the uppersurface of JFET 120 between source/drain regions 132, 134 can result ina reduction (about 50%) of the area required to form JFET 120, ascompared to JFET 20. The configuration of JFET 120 shown in FIG. 2 canalso reduce an effective channel length between source region 132 anddrain region 134, which reduces the R_(on) for JFET 120, as compared toJFET 20. STI region 136 can also help maintain a low pinch off voltage,V_(p) (as compared to JFET 20) because STI region 136 provides a deeppedestal, or wedge, which decreases the vertical depletion distancerequired for lower gate 124 to pinch-off channel region 126.

FIG. 3 shows a JFET 220 according to another embodiment of thisinvention. JFET 220 is similar to JFET 120 in that it includes a deepdoped region 222, a lower gate 224 and a channel region 226. JFET 220further includes a source region 232 having an upper surfacesubstantially coplanar with the upper surface of JFET 220, the uppersurface of source region 232 having an inner edge 232 a and an outeredge 232 b. JFET 220 further includes a drain region 234 having an uppersurface substantially coplanar with the upper surface of JFET 220, theupper surface of drain region 234 having an inner edge 234 a and anouter edge 234 b.

Similar to JFET 120, JFET 220 does not include an upper gate coplanarwith the upper (top) surface of JFET 220, and instead includes a single,uninterrupted STI region 236 with an upper surface substantiallycoplanar with the upper surface of JFET 120, wherein STI region 236extends from inner edge 132 a of source region 132 to inner edge 134 aof drain region 134. As such, there is no upper gate, i.e.,intentionally doped region between inner edge 132 a of source region 132and inner edge 134 a of drain region 134.

STI region 236 can comprise any now known or later developed insulatormaterial, and can be formed by any commonly known technique for formingan isolation region, such as etching a pattern of trenches in thesilicon, depositing one or more dielectric materials (such as siliconoxide) to fill the trenches, and removing the excess dielectric using atechnique such as chemical-mechanical planarization.

JFET 220 further includes an asymmetrical quasi-buried upper gate 238 inchannel region 226. As illustrated in FIG. 3, quasi-buried upper gate238 is disposed under STI region 236, not coplanar with an upper surfaceof JFET 220, as in traditional JFETs (see, e.g., JFET 20 shown in FIG.1). Quasi-buried upper gate 238 can be asymmetric, e.g., it can bepositioned only under a portion of STI region 236 which is proximate tosource region 232, while not extending under a portion of STI region 236which is proximate to drain region 234. Alternatively, as shown in FIG.3, quasi-buried upper gate 238 can be positioned partially under STIregion 236, and along a sidewall of STI region 236 proximate to sourceregion 232.

FIG. 4 further illustrates the position of quasi-buried upper gate 238,showing a top down view of JFET 220. As is shown, quasi-buried uppergate 238 extends partially under STI region 236, and partially undersource region 232, but not under drain region 234. In other words,quasi-buried upper gate 238 is not only held off drain region 234, butalso does not extend under a portion of STI region 236 that is proximateto drain region 234. Because quasi-buried upper gate 238 is depositedonly under a portion of STI region 236, it is referred to asasymmetrical. As shown in FIG. 3, in one embodiment, quasi-buried uppergate 238 encroaches up a substantially vertical sidewall of STI region236 proximate to source region 232, but not up a substantially verticalsidewall of STI region 236 proximate to drain region 234.

Excluding quasi-buried upper gate 228 from extending under the portionSTI region 236 that is proximate to drain region 234 or under drainregion 234, does not degrade the drain to gate (V_(dg)) breakdownvoltage. FIG. 5 shows a cross-sectional view along the x-axis of FIG. 4,enlarged to better illustrate quasi-buried upper gate 238.

As shown in FIGS. 4 and 5, according to another embodiment of theinvention, an implantation layer 240, e.g., to reduce R_(on), can beincluded under source region 232. R_(on) reduction implantation layer240 is a higher n-doped portion of channel region 226 only under sourceregion 232. R_(on) reduction implantation layer 240 is considered higherdoped because there are more n-type dopants located in this region thanremaining channel region 226. The higher doped nature of implantationlayer 240 will act to reduce the vertical series resistance from asurface of a contact (not shown) to source region 232 down to the bottomof STI region 236. This will effectively reduce R_(on) for the entireJFET 220. A depth of implantation layer 240 can be modified as desiredfor a given R_(on), source to gate (V_(sg)) breakdown voltage and sourceto gate parasitic capacitance (C_(sg)). In general, the deeperimplantation layer 240 extends into JFET 220, the lower source region232 series resistance will be, but the higher the C_(sg) will be.

FIG. 6 shows a cross-sectional view along the y-axis of FIG. 4, enlargedto better illustrate quasi-buried upper gate 238. As FIG. 6 shows, awell/sidewall gate contact 244 can be formed as a reach-through contactto lower gate 224, and an upper gate contact 242 can be formed tocontact quasi-buried upper gate 238. Contacts 242, 244 are similarlydoped regions as quasi-buried upper gate 238 and lower gate 224. Uppergate contact 242 can be a highly doped region contacting a surface ofsubstrate 210 and quasi-buried upper gate 238. FIG. 4 also shows uppergate contact 242 in a different view.

The term “doping” used herein refers to a process of intentionallyintroducing impurities into substrate to change its electricalproperties, for example, by ion implantation, shown in the figures by aseries of arrows. The term “highly doped” as used in connection withembodiments of this invention refers to commonly understoodmetal-oxide-semiconductor field effect transistor (MOSFET) source/drainimplants, i.e., approximately 1E15 to 1E16 atoms/cm² or concentration of1E20 to 1E21 atoms/cm³ dopant concentration.

A method of forming JFET 220 is shown in FIGS. 7A-15B. The “A” drawingsof FIGS. 7A-15B show method steps along the x-axis of JFET 220 (FIG. 4),while the “B” drawings of FIGS. 7A-15B show method steps along they-axis of JFET 220 (FIG. 4).

Turning to FIGS. 7A and 7B, substrate 210 is provided (doped with p-typedopants in this example, but as it is understood that p-type and n-typedopants shown and discussed herein can be reversed). Substrate 210 cancomprise any commonly used substrate material including but not limitedto silicon, germanium, silicon germanium, silicon carbide, and thosecomprising essentially of one or more III-V compound semiconductorshaving a composition defined by the formula AlX1GaX2InX3AsY1PY2NY3SbY4,where X1, X2, X3, Y1, Y2, Y3, and Y4 represent relative proportions,each greater than or equal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 beingthe total relative mole quantity). Other suitable substrates includeII-VI compound semiconductors having a composition ZnA1CdA2SeB1TeB2,where A1, A2, B1, and B2 are relative proportions each greater than orequal to zero and A1+A2+B1+B2=1 (1 being a total mole quantity).Furthermore, a portion or an entire semiconductor substrate may bestrained.

As shown in FIGS. 7A and 7B, a trench 235 is etched in the surface ofsubstrate 210 which will become shallow trench isolation (STI) region236 (FIGS. 2-6). Trench 235 has a substantially horizontal bottomsurface 235 b, a substantially vertical source side 235 c and asubstantially vertical drain side 235 a. P-type dopants are thenimplanted to create a p-type quasi-buried upper gate 238 under trench235. As shown in FIG. 7A, quasi-buried upper gate 238 extends onlypartially along bottom surface 235 b of trench 235, i.e., quasi-buriedupper gate 238 is not implanted along at least a portion of bottomsurface 235 b of trench 235 or along substantially vertical drain side235 a. Quasi-buried upper gate 238 can have a doped concentration in therange of 1E18 to 1E21 atom/cm³. Quasi-buried upper gate 238 has a higherdoped concentration than channel region 226 in order to over compensateand still maintain opposite polarity type from channel region 226.

As discussed herein, quasi-buried upper gate 238 is only under trench235 (ultimately STI region 236) proximate to source region 232, and notproximate to drain region 234. For example, quasi-buried upper gate 238can be included along only a portion of bottom surface 235 b, and alongonly one sidewall of trench 235, i.e., substantially vertical sourceside 235 c and not substantially vertical drain side 235 a. Therefore, amask, such as mask 410, can be applied to block certain areas adjacentto trench 235 from being implanted. For example, a photoresist material420 can be used to block substantially vertical drain side 235 a and aportion of bottom surface 235 b of trench 235 from being implanted.

Mask 410 (and other masks discussed herein) can comprise a hard maskdielectric material, such as a combination of silicon oxide and nitride,commonly used during STI processing. During STI processing, mask 410acts as hardmask protection during an RIE trench etch, but can also beused as a stop during chemical mechanical polishing (CMP) whenplanarizing the dielectric fill material for STI. This can be helpfulfor JFET processing because mask 410 provides a self aligned processwhich blocks the implant from a top surface of substrate 210 but allowsthe implant to go into a bottom of a trench, and possibly on thesidewalls depending on STI sidewall angle/profile and/or the angle ofthe implant.

Once quasi-buried upper gate 238 has been formed, standard JFETprocessing can continue. For example, as shown in FIGS. 8A and 8B,trench 236 is filled with isolation material to create STI region 236.STI region 236 can be formed by any commonly known technique for formingan isolation region, such as etching a pattern of trenches in thesilicon, depositing one or more dielectric materials (such as siliconoxide) to fill the trenches, and removing the excess dielectric using atechnique such as chemical-mechanical planarization. Commonly usedinsulating material can be used for STI region 236, i.e, any dielectricfilm that provides electrical isolation, including, but not limited tosilicon oxide or silicon nitride and/or a combination of silicon oxideand silicon nitride.

N-type dopants are then implanted to form deep isolation layer 222. Itis understood that deep isolation layer 222 is only needed for n-channeldevices. Deep isolation layer 222 can be at any desired depth, as longas it is deep enough to allow regions (discussed herein) to be formedabove layer 222 and under STI region 236.

Next, as shown in FIGS. 9A and 9B, a mask 430 is applied so that p-typedopants are implanted in the desired region to form lower gate 224.Implant dosage to form lower gate 224 can be in a range from 1E16 to1E20 atom/cm³. Then, as shown in FIGS. 10A and 10B, a mask 440 isapplied such that n-type dopants are implanted in the desired region toform channel region 226 surrounding STI region 236. In one embodiment,lower gate 224 is higher doped than channel region 226 in order to overcompensate and still maintain opposite polarity type from channel region226.

FIGS. 11A and 11B show the formation of well/sidewall gate contact 244to contact lower gate 224. A mask 450 is applied to block the rest ofthe surface of JFET 220 while well/sidewall gate contact 244 is formedadjacent to STI region 236 by implanting p-type dopants. While only onewell/sidewall gate contact 244 is shown in FIG. 11B, it is understoodthat additional contacts can be formed to contact lower gate 224.

FIGS. 12A and 12B show the formation of implantation layer 240 to reduceR_(on). R_(on) reduction implantation layer 240 is a highly n-dopedportion of channel region 226. A mask 460 is applied to ensure thatR_(on) reduction implantation layer 240 is formed on only one side ofSTI region 236, e.g., a side that will ultimately be under source region232.

FIGS. 13A and 13B show the use of a mask 470 to create source region 232and drain region 234, where both source region 232 and drain region 234are adjacent to the same STI region 236. High dosed n-type dopants canbe used to implant source region 232 and drain region 234, for example,implant dosage in a range from approximately 1E18 to 1E21 atom/cm³,typically in range of approximately 1E20 to 1E21 atom/cm³. Source region232 and drain region 234 can therefore be higher doped than channelregion 226.

FIGS. 14A and 14B show the formation of upper gate contact 242 forcontacting quasi-buried upper gate 238. A mask 480 is applied to createupper gate contact 242 as desired. High dosed p-type dopants can be usedto implant upper gate contact 242, i.e., implant dosage in a range fromapproximately 1E18 to 1E21 atom/cm³, typically in range of approximately1E20 to 1E21 atom/cm³.

FIGS. 15A and 15B show a layer of silicide 246 formed over source region232, drain region 234, and gate contact region 242 so that standardmetallization processes can occur and have desirable ohmic contact downto substrate surface regions. Silicide layer 246 may be formed using anynow known or later developed technique, e.g., depositing a metal such astitanium, nickel, cobalt, etc., annealing to have the metal react withsilicon, and removing unreacted metal.

Spacers and source/drain extensions can also be formed. Again, thesespacers and source/drain extensions are not shown in the figures, as itis not necessary for illustrating the embodiments of this invention, butit is understood that the inclusion of spacers and source/drainextensions is commonly known in the art when working with MOSFETdevices.

It is also understood that several diffusion or annealing steps can beperformed throughout the process discussed above, as would be understoodby one of ordinary skill in the art. Such diffusion or annealing stepswould be performed to smooth out the layers and regions discussed hereinand to drive in the dopants to ensure that the layers are effective anddopants are electrically active.

While FIGS. 7A-15B show methodology to form JFET 220 with no upper gatecoplanar with the upper surface of JFET 220, quasi-buried upper gate 238and R_(on) reduction implantation layer 240, it is understood that asimilar process could be performed to form JFET 220 with no upper gatecoplanar with the upper surface of JFET 220, no quasi-buried upper gate,and with no R_(on) reduction implantation layer. In addition, similarmethodology can be employed to form JFET 220 with no upper gate coplanarwith the upper surface of JFET 220, no R_(on) reduction implantationlayer, but including quasi-buried upper gate 238.

As used herein, the term “depositing” may include any now known or laterdeveloped techniques appropriate for the material to be depositedincluding but are not limited to, for example: chemical vapor deposition(CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD),semi-atmosphere CVD (SACVD) and high density plasma CVD (HDPCVD), rapidthermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited reactionprocessing CVD (LRPCVD), metalorganic CVD (MOCVD), sputteringdeposition, ion beam deposition, electron beam deposition,laser-assisted deposition, thermal oxidation, thermal nitridation,spin-on methods, physical vapor deposition (PVD), atomic layerdeposition (ALD), chemical oxidation, molecular beam epitaxy (MBE),plating, evaporation, etc.

It is also understood that when discussing p-type and n-type dopingherein, the polarities can be reversed from what is disclosed, as longas adjacent layer are intentionally doped with an opposite polarity inorder to ensure that there is little to no conduction between thelayers.

FIG. 16 shows a block diagram of an exemplary design flow 900 used forexample, in semiconductor IC logic design, simulation, test, layout, andmanufacture. Design flow 900 includes processes, machines and/ormechanisms for processing design structures or devices to generatelogically or otherwise functionally equivalent representations of thedesign structures and/or devices described above and shown in FIGS. 2-6.The design structures processed and/or generated by design flow 900 maybe encoded on machine-readable transmission or storage media to includedata and/or instructions that when executed or otherwise processed on adata processing system generate a logically, structurally, mechanically,or otherwise functionally equivalent representation of hardwarecomponents, circuits, devices, or systems. Machines include, but are notlimited to, any machine used in an IC design process, such as designing,manufacturing, or simulating a circuit, component, device, or system.For example, machines may include: lithography machines, machines and/orequipment for generating masks (e.g. e-beam writers), computers orequipment for simulating design structures, any apparatus used in themanufacturing or test process, or any machines for programmingfunctionally equivalent representations of the design structures intoany medium (e.g. a machine for programming a programmable gate array).

Design flow 900 may vary depending on the type of representation beingdesigned. For example, a design flow 900 for building an applicationspecific IC (ASIC) may differ from a design flow 900 for designing astandard component or from a design flow 900 for instantiating thedesign into a programmable array, for example a programmable gate array(PGA) or a field programmable gate array (FPGA) offered by Altera® Inc.or Xilinx® Inc.

FIG. 16 illustrates multiple such design structures including an inputdesign structure 920 that is preferably processed by a design process910. Design structure 920 may be a logical simulation design structuregenerated and processed by design process 910 to produce a logicallyequivalent functional representation of a hardware device. Designstructure 920 may also or alternatively comprise data and/or programinstructions that when processed by design process 910, generate afunctional representation of the physical structure of a hardwaredevice. Whether representing functional and/or structural designfeatures, design structure 920 may be generated using electroniccomputer-aided design (ECAD) such as implemented by a coredeveloper/designer. When encoded on a machine-readable datatransmission, gate array, or storage medium, design structure 920 may beaccessed and processed by one or more hardware and/or software moduleswithin design process 910 to simulate or otherwise functionallyrepresent an electronic component, circuit, electronic or logic module,apparatus, device, or system such as those shown in FIGS. 2-6. As such,design structure 920 may comprise files or other data structuresincluding human and/or machine-readable source code, compiledstructures, and computer-executable code structures that when processedby a design or simulation data processing system, functionally simulateor otherwise represent circuits or other levels of hardware logicdesign. Such data structures may include hardware-description language(HDL) design entities or other data structures conforming to and/orcompatible with lower-level HDL design languages such as Verilog andVHDL, and/or higher level design languages such as C or C++.

Design process 910 preferably employs and incorporates hardware and/orsoftware modules for synthesizing, translating, or otherwise processinga design/simulation functional equivalent of the components, circuits,devices, or logic structures shown in FIGS. 2-6 to generate a netlist980 which may contain design structures such as design structure 920.Netlist 980 may comprise, for example, compiled or otherwise processeddata structures representing a list of wires, discrete components, logicgates, control circuits, I/O devices, models, etc. that describes theconnections to other elements and circuits in an integrated circuitdesign. Netlist 980 may be synthesized using an iterative process inwhich netlist 980 is resynthesized one or more times depending on designspecifications and parameters for the device. As with other designstructure types described herein, netlist 980 may be recorded on amachine-readable data storage medium or programmed into a programmablegate array. The medium may be a non-volatile storage medium such as amagnetic or optical disk drive, a programmable gate array, a compactflash, or other flash memory. Additionally, or in the alternative, themedium may be a system or cache memory, buffer space, or electrically oroptically conductive devices and materials on which data packets may betransmitted and intermediately stored via the Internet, or othernetworking suitable means.

Design process 910 may include hardware and software modules forprocessing a variety of input data structure types including netlist980. Such data structure types may reside, for example, within libraryelements 930 and include a set of commonly used elements, circuits, anddevices, including models, layouts, and symbolic representations, for agiven manufacturing technology (e.g., different technology nodes, 32 nm,45 nm, 90 nm, etc.). The data structure types may further include designspecifications 940, characterization data 950, verification data 960,design rules 970, and test data files 985 which may include input testpatterns, output test results, and other testing information. Designprocess 910 may further include, for example, standard mechanical designprocesses such as stress analysis, thermal analysis, mechanical eventsimulation, process simulation for operations such as casting, molding,and die press forming, etc. One of ordinary skill in the art ofmechanical design can appreciate the extent of possible mechanicaldesign tools and applications used in design process 910 withoutdeviating from the scope and spirit of the invention. Design process 910may also include modules for performing standard circuit designprocesses such as timing analysis, verification, design rule checking,place and route operations, etc.

Design process 910 employs and incorporates logic and physical designtools such as HDL compilers and simulation model build tools to processdesign structure 920 together with some or all of the depictedsupporting data structures along with any additional mechanical designor data (if applicable), to generate a second design structure 990.Design structure 990 resides on a storage medium or programmable gatearray in a data format used for the exchange of data of mechanicaldevices and structures (e.g. information stored in a IGES, DXF,Parasolid XT, JT, DRG, or any other suitable format for storing orrendering such mechanical design structures). Similar to designstructure 920, design structure 990 preferably comprises one or morefiles, data structures, or other computer-encoded data or instructionsthat reside on transmission or data storage media and that whenprocessed by an ECAD system generate a logically or otherwisefunctionally equivalent form of one or more of the embodiments of theinvention shown in FIGS. 2-6. In one embodiment, design structure 990may comprise a compiled, executable HDL simulation model thatfunctionally simulates the devices shown in FIGS. 2-6.

Design structure 990 may also employ a data format used for the exchangeof layout data of integrated circuits and/or symbolic data format (e.g.information stored in a GDSII (GDS2), GL1, OASIS, map files, or anyother suitable format for storing such design data structures). Designstructure 990 may comprise information such as, for example, symbolicdata, map files, test data files, design content files, manufacturingdata, layout parameters, wires, levels of metal, vias, shapes, data forrouting through the manufacturing line, and any other data required by amanufacturer or other designer/developer to produce a device orstructure as described above and shown in FIGS. 2-6. Design structure990 may then proceed to a stage 995 where, for example, design structure990: proceeds to tape-out, is released to manufacturing, is released toa mask house, is sent to another design house, is sent back to thecustomer, etc.

The circuit as described above is part of the design for an integratedcircuit chip. The chip design is created in a graphical computerprogramming language, and stored in a computer storage medium (such as adisk, tape, physical hard drive, or virtual hard drive such as in astorage access network). If the designer does not fabricate chips or thephotolithographic masks used to fabricate chips, the designer transmitsthe resulting design by physical means (e.g., by providing a copy of thestorage medium storing the design) or electronically (e.g., through theInternet) to such entities, directly or indirectly. The stored design isthen converted into the appropriate format (e.g., GDSII) for thefabrication of photolithographic masks, which typically include multiplecopies of the chip design in question that are to be formed on a wafer.The photolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

The method as described above is used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

While various embodiments are described herein, it will be appreciatedfrom the specification that various combinations of elements, variationsor improvements therein may be made by those skilled in the art, and arewithin the scope of the invention. In addition, many modifications maybe made to adapt a particular situation or material to the teachings ofthe invention without departing from essential scope thereof. Therefore,it is intended that the invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thisinvention, but that the invention will include all embodiments fallingwithin the scope of the appended claims.

What is claimed is:
 1. A method of forming a junction field effecttransistor (JFET), the method comprising: forming a trench in thesubstrate, the trench having a substantially horizontal bottom surface,a substantially vertical first side and a substantially vertical secondside; forming a quasi-buried upper gate below the trench; filling thetrench with an insulator material to create a shallow trench isolation(STI) region, wherein the quasi-buried upper gate is disposed such thatonly a portion of the quasi-buried upper gate is positioned under aportion of the STI region such that the quasi-buried upper gate does notextend along a portion of the STI region proximate to the second side ofthe trench; forming a lower gate region below the STI region; forming achannel region disposed between the lower gate and the STI region;forming a source region adjacent to the first side of the STI region;and forming a drain region adjacent to the second side of the STIregion.
 2. The method of claim 1, wherein the quasi-buried upper gateextends at least partially along the substantially vertical first sideof the STI region.
 3. The method of claim 1, wherein the forming of thequasi-buried upper gate comprises ion implanting.
 4. The method of claim1, further comprising forming an implantation layer in the channelregion only under the source region, wherein the implantation layerincludes a higher concentration of dopants than the channel region. 5.The method of claim 1, further comprising forming a doped quasi-buriedupper gate contact to the quasi-buried upper gate, wherein thequasi-buried upper gate contact has a dopant concentration in the rangeof approximately 1E18 to approximately 1E21 atom/cm³.
 6. The method ofclaim 1, wherein the quasi-buried upper gate has a dopant concentrationin the range of approximately 1E18 to approximately 1E21 atom/cm³. 7.The method of claim 1, wherein the quasi-buried upper gate has a higherconcentration of dopants than the channel region.
 8. The method of claim1, wherein the lower gate region has a dopant concentration in the rangeof approximately 1E16 to approximately 1E20 atom/cm³.
 9. The method ofclaim 5, further comprising forming a silicide layer disposed above thesource region, the drain region, and the quasi-buried upper gatecontact.